Rb Doping and Lattice Strain Synergistically Engineering Oxygen Vacancies in TiO₂ for Stable High‐Contrast Photoreversible Color Switching

Abstract The utilization of TiO 2 for the fabrication of transparent photochromic materials is both cost‐effective and environmentally friendly. However, it still poses challenges due to the rapid recombination of electron‐hole pairs and poor organic‐inorganic compatibility. Oxygen vacancies play a crucial role in sustaining sacrificial electron donors for hole scavenging, demonstrating great potential in enhancing photochromic performance. Herein, Rb doping and lattice strain are applied to synergistically engineer oxygen vacancies, considering lattice oxygen release is influenced by charge neutrality and oxygen atom coordination environment. Furthermore, the particle surface is modified using composite siloxanes to ensure monodispersion and enhance organic‐inorganic compatibility. Structural analyses and theoretical calculations indicate that Rb doping and epitaxial strain synergistically reduce the oxygen vacancy formation energy and promote the chemical adsorption of diethylene glycol (DEG) on the TiO 2 surface for hole scavenging. The designed DEG‐added Rb‐TiO 2 /TB‐CS (TB means extra titanium butoxide, CS means composite siloxanes) nanodispersion exhibits a significant optical modulation amplitude exceeding 90% at 650 nm, rapid response within 60 s, and stable reversibility in color‐switching (50 cycles). Moreover, utilizing Rb‐TiO 2 /TB‐CS with DEG ligands as a responsive material enables the fabrication of transparent photochromic polyacrylate‐based hybrid films, polyvinyl alcohol‐based hydrogels, and hydroxyethyl cellulose‐based rewritable papers, showcasing its immense potential for diverse applications.